A. Field of the Invention
The present invention is for a prosthetic foot having a flexible plantar member, a flexible dorsal member, and a posterior pylon member connected by ball and socket joints. Elastic snubbers and torsion resistors are positioned in between the plantar member and the dorsal member to aid in controlling the movement of the three structural members relative to each other. During ambulation, the design of the foot including the various ball and socket joints combined with the various elastic members function to allow the foot to deform elastically to generate approximately the same forces and feel to the user as would be generated by the skeleton, muscles, tendons, and ligaments of a natural foot.
B. Description of the Related Art
Artificial limbs and particularly prosthetic feet and legs have been known for centuries. The earliest were probably similar to the crude wooden "peg legs." These early devices enabled the user to stand and to walk awkwardly, usually with the additional aid of a crutch or cane.
In the early 20th century designers of artificial or prosthetic feet first attempted to duplicate the appearance and function of a natural foot. During the ensuing 70 or 80 years, the designs for prosthetic feet have remained relatively unchanged. What changes did occur seemed to come mainly from improvements in available materials. Classic prosthetic feet used spring principles to cushion shocks due to walking and running and allow some degree of movement of the foot. U.S. Pat. No. 1,294,632 to Dickson discloses such an artificial foot. More versions of the spring foot also known as an energy storing foot, are disclosed in U.S. Pat. No. 4,547,913, 4,645,509, and 4,822,363.
These devices have come to be known as energy storing feet because as the springs are deflected they store energy which is largely returned to the user as the foot elastically returns to its undeformed shape. The obvious disadvantages to such prosthetic devices are that springs alone poorly duplicate the deflections, forces, and feel to the user of a natural foot.
Designers have attempted to more closely approximate the action of a natural foot by adding ball and socket ankle joints geometrically similar to a natural anatomical ankle. Feet incorporating simulated ankle joints do theoretically allow for more natural movement, but copying the anatomical joint itself is not enough. Without all of the muscles, tendons, and cooperating bone structure of an anatomical foot, the anatomical type ankle joint is too unstable to be practical. Attempts to stabilize prosthetic ball and socket ankle joints are shown in U.S. Pat. Nos. 4,461,045 and 4,463,459, both issued to Shorter et al.